Stages of embryonic development and changes in enzyme activities in embryogenesis of turbot (Scophthalmus maximus L.)

The early development of turbot (Scophthalmus maximus) from fertilization to hatching was described. Hatching occurred at 108 h post-fertilization (hpf) in 14 A degrees C. Yolk syncytial layer and blastocoel formed at morula stage and low stage, respectively. Neural rod derived from the ectoderm appeared and the first somite formed in the middle of the embryonic body at 90 % epiboly stage, and notochord primordium formed at complete epiboly stage. Kupffer's vesicle appeared at 59 h 35 min hpf and degenerated at 89 hpf. At 72 hpf, the digestive tract formed in the ventral side of the embryonic body, and the posterior digestive tract of embryo was ciliated at 89 hpf. Enzymes play a key role in the catabolism of yolk during embryogenesis of fishes. In this study, the main enzymes alkaline phosphatase (AP), leucine aminopeptidase N (LAP), pepsin, trypsin and Leucine-alanine peptidase (Leu-ala) were all observed in unfertilized eggs and embryo of S. maximus, but amylase was not detected, speculating that amino acids appear to be the main energy substrate during embryonic development of S. maximus, while carbohydrates is less essential. AP reached the lowest value at the gastrula stage and then increased rapidly reaching the highest value at hatching. LAP showed the highest value in unfertilized eggs and kept on decreasing until the blastula stage with the lowest value and then increased at the gastrula stage, followed by a gradual decline thereafter. Trypsin reached the lowest value at the blastula stage and then fluctuated with the maximal value at hatching. Pepsin reached the highest and the lowest values at the unfertilized eggs and the cleavage stage, respectively, but disappeared at hatching. Leu-ala had the maximum activity at the blastula stage and then declined to the minimum at the gastrula stage followed by a gradual increase thereafter.